Within the field of audio reproduction, such as hi-fi stereo or surround sound systems for home use, it is well-known to apply a pre-equalizing to compensate sound reproduction for the coloration introduced by the listening room, or rather by an interaction between the loudspeaker and the listening room. Different approaches have been made to provide an improved sound reproduction quality with a more neutral timbre when listening to a loudspeaker in a given position in a given room.
Prior art solutions include methods based on a measurement of transfer characteristics from the loudspeaker to the listening position and then designing a filter compensating for this transfer characteristic. This has a number of well-known disadvantages such as uncontrolled high gains at specific low frequencies due to the presence of room modes, unless a number of additional modifications are performed. Still, these type of equalizing methods may result in a sound reproduction outside the listening position which has a more severe coloration than without the equalizing. Even very small movements outside the listening position, such as few centimetres, may in some cases be enough to degrade the perceived sound quality significantly. An example of a single point equalizing approach can be seen in U.S. Pat. No. 4,458,362.
As an alternative, several prior art methods suggest averaging transfer characteristics measured in a number of positions in the vicinity of the listening position so as to provide an equalizing which will provide satisfactory results for a larger listening area. However, such methods often require a quite large number of measurements, and still provide quite poor results when a listener moves outside a quite narrow listening area. Thus, in order for such methods to work in general, a large number of manual corrections are needed by a skilled operator. An example of a multi-point equalizing approach can be seen in U.S. Pat. No. 6,760,451.
Still other equalizing methods exist that are based on estimating a general acoustic response from the loudspeaker in the room, i.e. away from the listening position. This can either be done by averaging measurements performed in a number of positions in the room, or alternatively by measuring a power output from the loudspeaker or an equivalent acoustic parameter such as radiation resistance as described in EP 0 772 374 B1.